PROJECT SUMMARY Fibrosis is a detrimental component of many interstitial lung diseases. Idiopathic pulmonary fibrosis (IPF) is a particularly deadly disorder for which there are few treatment options, largely because the mechanisms governing the progression of pulmonary fibrosis are poorly understood. One of the more striking observations in IPF is the robust over-expression of fibrotic mediators and matrix components that contribute to the unremitting fibrotic response in the lungs. This over-active mediator response is in part responsible for the uncontrollable progression of this disease. The mechanisms behind the robust over-expression of fibrotic mediators in IPF have been elusive; however, during the previous funding period of this grant we discovered that a cellular process known as Alternative Polyadenylation (APA) may account for the excessive over-production of fibrotic mediators in IPF. APA regulates the length of the 3' end of mRNAs and in so doing can render them resistant to the repressive effects of microRNAs. This process results in the amplified translation of these mRNAs. We have recently found that a protein that regulates APA, known as cleavage factor 25 (CFlm25), is down-regulated in the lungs of patients with IPF. Moreover, CFlm25 down-regulation was found to be robust in myofibroblasts, key cells known to produce fibrotic mediators. These findings have led to the hypothesis that down-regulation of CFIm25 in fibrotic environments amplifies pulmonary fibrosis by up-regulating pro-fibrotic gene expression through APA. We will test this hypothesis in the following specific aims: Aim 1: Characterize CFIm25- dependent APA in humans and mice with pulmonary fibrosis. Aim 2: Evaluate the in vivo role of CFIm25 in pulmonary fibrosis. and Aim 3: Determine the mechanisms responsible for the down-regulation of CFIm25 and assess their potential as therapeutic targets in pulmonary fibrosis. Collectively, these studies will enhance our knowledge of a novel mechanism of pro-fibrotic gene expression that could account for the excessive amplification of pro-fibrotic proteins in IPF. This research will lay the foundation for identifying agents to block this pathway as an approach to stop the progression of this deadly disease.